Efforts to relieve the worldwide shortages of protein have included various biosynthesis processes. Biologically produced single cell protein (SCP) has been obtained by the growth of a variety of microorganisms including bacteria, yeast and fungi on a variety of carbon-containing substrates. Petroleum hydrocarbons have been employed as a carbon and energy source, but have faced practical difficulties in the lack of water solubility, and in the high consumption of oxygen to assist in the microbial conversion. Other processes have centered on the use of oxygenated hydrocarbon derivatives as feedstocks due to the inherent water solubility of such feedstocks, and hence the ease of handling since microbial conversion processes are essentially conducted under aqueous conditions.
Aerobic microbial conversions are highly exothermic oxidation reactions which demand large quantities of molecular oxygen, and which produce large quantities of heat. The heat must be removed continuously and consistently, or risk overheating of the system and death of the microorganisms, or at least severe limitations on growth of the microorganisms as temperatures rise, and hence severe reductions in efficiencies. Consistant constant supplies of molecular oxygen are necessary to maintain high fermentation efficiencies, and at the same time to assist in providing good heat transfer.
To maintain high fermentation efficiencies in commercial fermentations, oxygen is supplied as a molecular oxygen-containing gas free of any stray microorganisms into the culture media under conditions to provide maximum contact of the oxygen with the culture media so as to dissolve as much oxygen into the aqueous media as possible, as well as to assist in providing heat transfer.
High oxygen transfer rates have been achieved heretofore by conducting a fermentation process as a foam-type process to assist in achieving a high surface area for contact between the liquid phase and the gas phase, in order to obtain a high rate of oxygen transfer from the gas phase into the aqueous phase, and at the same time to assist in obtaining a good rate of removal of carbon dioxide, a natural consequence of aerobic fermentation processes, and heat from the aqueous medium to the gas phase which then is exhausted for such use as may be suitable.
There is a continuing need for improved apparatus suitable for conducting aerobic fermentation processes with high oxygen transfer rates and to provide effective contact between the aqueous medium and the oxygen-containing gas phase, and at the same time, provide an apparatus which is basically straightforward in construction, economical to manufacture and maintain, and yet well adapted for its intended use.